1. Field of the Invention
The present invention relates to a characteristic correction system for an automatic transmission, which is capable of obtaining a favorable shift quality by correcting characteristic variation among individual transmissions.
2. Description of the Related Art
Component tolerance typically exists in each constitutional element of an automatic transmission installed in a vehicle such as an automobile, and therefore slight variation in the characteristics of the transmission in its final assembled state due to individual differences is inevitable. To improve the performance of the vehicle, the amount of variation must be suppressed as much as possible, but at the same time, reducing tolerance while ensuring process capability in a production factory may lead to repercussions such as cost increases.
In a so-called direct AT system automatic transmission which controls the engagement (or in other words the oil pressure) of engagement elements such as clutches and brakes by providing each engagement element with a solenoid valve, variation in the shift quality is particularly likely to occur due to manufacturing irregularities in the solenoid valves and engagement elements, deterioration thereof with age, friction, and so on. To reduce this variation in the shift quality and obtain a stable, favorable shift quality, learning control is typically performed during actual travel. However, a considerable amount of actual travel time is required to secure a favorable shift quality through learning control.
Hence, Japanese Unexamined Patent Application Publication No. 2003-14119 proposes a technique that is executed during a test performed on a transmission prior to installation in a vehicle, in which a drive signal applied to a solenoid valve of a hydraulic control device, piston stroke data and engagement pressure data relating to a hydraulic servo for operating an engagement element of the transmission, and so on are obtained as unique data and stored in a memory of an electronic control unit.
Further, in Japanese Unexamined Patent Application Publication No. 2004-286062, the present applicant proposes a technique of measuring a controlled variable of a hydraulic control valve, which maintains the difference between an input rotation speed and a turbine rotation speed of a torque converter at a fixed value, during a completion operation performed on an automatic transmission following assembly, and correcting characteristic variation among individual automatic transmissions on the basis of a difference between a measured value and a reference value of the controlled variable.
If characteristic variation in an automatic transmission is to be corrected without waiting for the promotion of learning through actual travel, it is desirable to be able to obtain data that are unique to each individual transmission and differences between the unique data and reference characteristics quickly and with stability in consideration of the factory task time at the product shipping stage, the time required for a market dealer to reset a learned value during inspection and repair by cutting the power of the electronic control device, and so on. In this regard, however, Japanese Unexamined Patent Application Publication No. 2003-14119 does not disclose a specific method of obtaining unique data, and although in Japanese Unexamined Patent Application Publication No. 2004-286062 a unique controlled variable of the transmission can be measured with stability, the measurement time tends to be long, leaving room for improvement.